Isocyanates are a substance class deriving from carbonic acid. Isocyanides can be described as instable carbamide acid (mono amide of carbonic acid which dissociates to ammonia and carbon dioxide). The isocyanates rapidly degrade into amines. With primary alcohol, isocyanates react to stable urethanes. Isocyanates are important for the plastics industry.
Technically, isocyanates are produced from synthesis of amines with phosgene. Two different principles can be differentiated: phosgenisation with free amines or phosgenisation with amine salts. Alternatively, di-isocyanates can be used for the isocyanate synthesis. Isocyanates show a high reactivity with reactive hydrogen. Due to this reason, on the one hand, the success and broad variety of chemical reactions can be explained. On the other hand, high toxicity and related side reactions also arise.
The addition reaction of isocyanates with hydrogen-active compounds is exothermic with a high reaction velocity. With water, isocyanates react more slowly. With amines the reaction time at room temperature is slow and carbon dioxide is eliminated. Aromatic isocyantes are more reactive than aliphatic isocyanates.
In addition to the addition reaction, isocyanates can polymerize H-active compounds. Depending on the individual reaction compounds and catalysts, the reaction results in linear polymers or cyclic di- or trimers. Isocyanates can trimerize with addition of alkali.
Due to the diversity of reactions it is necessary during polyurethane production to have an excess of isocyanate component. The formation of isocyanate products is reversible which is beneficial for the synthesis of blocked isocyanates. Generally, blocked isocyantes are an isocyanate, which has been transformed with a blocking reagent at elevated temperature in presence of a nucleophilic component into an isocyanate adduct. The first patents for isocyanate blocking derive from Schalck and Bunge 1939 and 1940. In comparison to the free isocyanates, the blocked isocyanates have significant advantages. They are less hazardous, less sensitive to hydrolytic reactions, easier for handle, easier to store and easier to transport. However, blocked isocyanates are also disadvantageous due to their difficulty in synthesis and associate costs in production.
The use of isocyanates in polymer production (in addition to the synthesis of blocked isocyanates) represents a significant disadvantage due to their toxicity to human users, the environment and the possibility of further chemical reactions with surrounding reactive materials.
The present invention relates to production methods for synthetic substances, for polymers and/or modified polyurethanes that avoid the likely risks of the conventional isocyanate use. Polyurethane bonding agents have excellent properties relating to stability during changes in temperature, to adhesion, as well as to stability against chemicals, humidity and solvents. Polyurethane materials are produced through polymerization reaction of a di-isocyanate with a di-alcohol and polyurethane-polyoles, which results in a multi-molecular cross-linked compound. A considerable disadvantage of such a polymerization reaction is the production of end products such as alcohols and isocyanates.
Isocyanates have a high level of reactivity, which is why they are used so successfully; but for that reason they are also toxic, being very likely to have a cancer generating effect. When isocyanates interact with H-active compounds, some of the products are also H-active and can, therefore, react with isocyanates as well. Research is needed to reduce the production of blocking agents and to avoid dangerous compounds like free isocyanates as well as phosgene. The goal of such research is to produce isocyanate-free polymer structures. When toxic isocyanates are used for the synthesis of polyurethane materials by conventional means, they remain a safety problem, since upon the hardening of the polymer network a certain amount of isocyanate material remains without having reacted with other materials. Hence the substitution of the isocyanates with non-poisonous cross-linking and/or adhesion materials is an important task.